The art of solid state devices has produced diodes, rectifiers and transistors of ever increasing current carrying capacities. The problem generally is to provide for the conductance of heat away from the solid state device at a sufficiently rapid rate to prevent the impairment or destruction of the device by heat, without the production of undesirable side effects, such as, for example, the transference of electromagnetic radiations to unwanted places. Many of the solid state devices of high current carrying capacity are enclosed in a metallic shell or housing including a mounting flange, this housing being connected electrically to one of the terminals of the solid device itself, so that this case or shell becomes a part of the circuitry in which the solid state device is operated. Accordingly, if radio frequencies are present in the circuitry or find their way into the circuitry they will appear at the housing or shell encasing the solid state device.
Most solutions of the heat dissipation problem have involved the mounting of the solid state devices on metal bodies called heat sinks which in many instances are a part of or are secured directly and individually to the chassis mounting the electronic apparatus of which the solid state device is a component, the chassis being provided with fins exposed exteriorly of the chassis and its enclosing cabinet, for dissipating the heat. In some instances, the solid state devices have been mounted on the outside of the chassis and cabinet combination, in order to associate them with the heat radiating fins. In the case of solid state devices having the metallic enclosing shell as a part of the circuitry, it becomes generally necessary to provide an insulating wafer between the shell of the solid state device and its heat sink, in order to prevent electrical conductivity between the solid state device and the mounting support. However, when radio frequency currents are present, they may pass from the shell of the solid state device to the mounting body through a non-metallic, capacitative coupling into unwanted places. Also, the inclusion of an insulating wafer or sheet between the shell of the solid state device and the heat sink body eliminates a metal-to-metal contact, whereas a metal-to-metal contact is desirable for the effective transference of heat.
Typical approaches to the solution of these problems are the disclosures of Trunk U.S. Pat. No. 3,261,396 granted July 19, 1966, Schneider U.S. Pat. No. 3,344,315 granted Sept. 26, 1967 and Reimer U.S. Pat. No. 3,780,798, granted Dec. 25, 1973. The Trunk patent shows a solid state device of the type having a combined enclosure shell and mounting flange which is secured in metal-to-metal contact with a plate of bare aluminum, to which are attached fins for radiating heat generated in the solid state device. The bare aluminum plate is secured to a metallic bracket, described as formed of aluminum with its surfaces anodized to provide a nonconductive film on which the heat sink body of aluminum is supported. The bracket is provided with punched ears for securing it on a chassis by means of fasteners such as screws. The Trunk patent contains no mention of the problem of suppressing radio frequency radiations but it will be apparent that there is a strong possibility of capacitive coupling of the heat sink plate to the mounting bracket through the thin layer of insulation provided by anodizing the bracket, and with the bracket provided with ears to rest upon a chassis and be secured thereto by screws there is a strong possibility of the transfer of such radiations to the mounting chassis and thence to a metallic enclosure for the chassis, either capacitively, or by direct metallic conductivity due to scratching of the thin insulating film on the bracket by careless use of tools.
As will be set forth more fully hereinafter, applicant's concept involves the mounting of solid state devices, whether diode, rectifier, or transistor, upon and with their enclosing metal shells directly in metallic contact with a heat sink body, and the provision of nonconductive supports for the heat sinks so arranged that the possibility of radiating electromagnetic energy into unwanted places, such as, primarily, a metallic cabinet enclosing the electronic apparatus, is negligible. The universality of applicant's concept to the different types of solid state devices as named in the preceding sentence contrasts importantly with the disclosure of the hereinbefore identified Schneider patent which discloses an arrangement for stacking, with intervening insulating elements, heat sink members in which diodes having threaded mounting studs are mounted, the heat sinks being surmounted by heat radiating fin structure. These heat sink members which have a configuration to accept only one type of semiconductor are stacked in a cabinet comprising an assemblage of a number of components including angle irons, sheet metal plates and tie rods. Applicant's concept includes the stacking of heat sinks provided with heat radiating fins but those heat sinks are adapted to mount any type of solid state device whereas those of Schneider are not. The significant differences between applicant's concept and those of Trunk and Schneider will become apparent from the following summary and detailed description of applicant's invention.
In addition, prior art devices do not provide efficient thermal conduction from semiconductor devices to heat radiating elements while still providing for the direct mounting of heat sink elements onto printed circuit boards. Thus, even with the use of insulating members between semiconductor devices and the heat sink of the present invention, the various embodiments of this invention provide direct mounting of the printed circuit board onto the heat sink block while still assuring adequate thermal flow from the semiconductor devices into the heat sink block and radiating member.
The requirement of most prior art devices that semiconductor devices requiring special heat sinks be separately mounted greatly increases the cost of assembly of electronic hardware. Thus, the prior art shows no overall assembly of printed circuit boards attached to inexpensive heat sink elements providing efficient thermal conductivity for heat generating electronic elements which may be easily mounted into a chassis for fan force air circulation over both the printed circuit board and the heat producing elements. Thus, although Reimer attaches a heat sink to a wiring card, his apparatus must rely upon convection air currents to dissipate the heat. Also, the fin arrangement provided by Reimer is expensive to manufacture and moreover does not provide a short heat conduction path between the heat susceptible components and the heat dissipating fins. In addition, the air passages provided by Reimer's fins are not exposed either to the heat susceptible components or the other electrical components attached to the wiring card. The prior art in general provides efficient cooling of semiconductor devices only at the expense of making the overall assembly of the electronic devices complex, expensive and time consuming and has not solved the problem of incorporating together the printed circuit board and efficient heat radiating elements to provide an inexpensive, efficient assembly for electronic hardware such as power supply units, switching units and power convertor units which must be designed to handle high electric currents while still providing sensitive control elements which do not handle large currents and are therefore not subjected to heat dissipation problems.